NCERT Solutions for Class 12 Science Chemistry Chapter 2 – Alcohols, Phenols And Ethers
Explore the comprehensive NCERT solutions for Class 12 Science Chemistry Chapter 2 – “Alcohols, Phenols, and Ethers” with straightforward, step-by-step explanations. These solutions have gained immense popularity among Chemistry students in class 12 Science, serving as valuable resources for completing homework efficiently and preparing for exams. All the questions and answers from the NCERT Book of Class 12 Science Chemistry Chapter 2 are available here at no cost, providing a convenient and accessible aid for students. Page No 317: Question 11.1: Classify the following as primary, secondary and tertiary alcohols: (i) (ii) (iii) (iv) (v) (vi) ANSWER: Primary alcohol → (i), (ii), (iii) Secondary alcohol → (iv), (v) Tertiary alcohol → (vi) Page No 317: Question 11.2: Identify allylic alcohols in the above examples. ANSWER: The alcohols given in (ii) and (vi) are allylic alcohols. Page No 320: Question 11.3: Name the following compounds according to IUPAC system. (i) (ii) (iii) (iv) (v) ANSWER: (i) 3-Chloromethyl-2-isopropylpentan-1-ol (ii) 2, 5-Dimethylhexane-1, 3-diol (iii) 3-Bromocyclohexanol (iv) Hex-1-en-3-ol (v) 2-Bromo-3-methylbut-2-en-1-ol Page No 325: Question 11.4: Show how are the following alcohols prepared by the reaction of a suitable Grignard reagent on methanal? (i) (ii) ANSWER: (i) (ii) Page No 325: Question 11.5: Write structures of the products of the following reactions: (i) (ii) (iii) ANSWER: (i) (ii) (iii) Page No 335: Question 11.6: Give structures of the products you would expect when each of the following alcohol reacts with (a) HCl-ZnCl2 (b) HBr and (c) SOCl2. (i) Butan-1-ol (ii) 2-Methylbutan-2-ol ANSWER: (a) (i) Primary alcohols do not react appreciably with Lucas’ reagent (HCl-ZnCl2) at room temperature. (ii) Tertiary alcohols react immediately with Lucas’ reagent. (b) (i) (ii) (c) (i) (ii) Page No 335: Question 11.7: Predict the major product of acid catalysed dehydration of (i) 1-Methylcyclohexanol and (ii) Butan-1-ol ANSWER: (ii) Page No 335: Question 11.8: Ortho and para nitrophenols are more acidic than phenol. Draw the resonance structures of the corresponding phenoxide ions. ANSWER: Resonance structure of the phenoxide ion Resonance structures of p-nitrophenoxide ion Resonance structures of o-nitrophenoxide ion It can be observed that the presence of nitro groups increases the stability of phenoxide ion. Page No 335: Question 11.9: Write the equations involved in the following reactions: (i) Reimer-Tiemann reaction (ii) Kolbe’s reaction ANSWER: Page No 342: Question 11.10: Write the reactions of Williamson synthesis of 2-ethoxy-3-methylpentane starting from ethanol and 3-methylpentan-2-ol. ANSWER: In Williamson synthesis, an alkyl halide reacts with an alkoxide ion. Also, it is an SN2 reaction. In the reaction, alkyl halides should be primary having the least steric hindrance. Hence, an alkyl halide is obtained from ethanol and alkoxide ion from 3-methylpentan-2-ol. Page No 342: Question 11.11: Which of the following is an appropriate set of reactants for the preparation of 1-methoxy-4-nitrobenzene and why? (i) (ii) ANSWER: Set (ii) is an appropriate set of reactants for the preparation of 1-methoxy-4-nitrobenzene. In set (i), sodium methoxide (CH3ONa) is a strong nucleophile as well as a strong base. Hence, an elimination reaction predominates over a substitution reaction. Page No 343: Question 11.12: Predict the products of the following reactions: (i) (ii) (iii) (iv) ANSWER: (i) (ii) (iii) (iv) Page No 344: Question 11.1: Write IUPAC names of the following compounds: (i) (ii) (iii) (iv) (v) (vi) (vii) (viii) (ix) (x) (xi) (xii) ANSWER: (i) 2, 2, 4-Trimethylpentan-3-ol (ii) 5-Ethylheptane-2, 4-diol (iii) Butane-2, 3-diol (iv) Propane-1, 2, 3-triol (v) 2-Methylphenol (vi) 4-Methylphenol (vii) 2, 5-Dimethylphenol (viii) 2, 6-Dimethylphenol (ix) 1-Methoxy-2-methylpropane (x) Ethoxybenzene (xi) 1-Phenoxyheptane (xii) 2-Ethoxybutane Page No 344: Question 11.2: Write structures of the compounds whose IUPAC names are as follows: (i) 2-Methylbutan-2-ol (ii) 1-Phenylpropan-2-ol (iii) 3,5-Dimethylhexane −1, 3, 5-triol (iv) 2,3 − Diethylphenol (v) 1 − Ethoxypropane (vi) 2-Ethoxy-3-methylpentane (vii) Cyclohexylmethanol (viii) 3-Cyclohexylpentan-3-ol (ix) Cyclopent-3-en-1-ol (x) 3-Chloromethylpentan-1-ol. ANSWER: (i) (ii) (iii) (iv) (v) (vi) (vii) (viii) (ix) (x) Page No 344: Question 11.3: (i) Draw the structures of all isomeric alcohols of molecular formula C5H12O and give their IUPAC names. (ii) Classify the isomers of alcohols in question 11.3 (i) as primary, secondary and tertiary alcohols. ANSWER: (i) The structures of all isomeric alcohols of molecular formula, C5H12O are shown below: (a) Pentan-1-ol (1°) (b) 2-Methylbutan-1-ol (1°) (c) 3-Methylbutan-1-ol (1°) (d) 2, 2-Dimethylpropan-1-ol (1°) (e) Pentan-2-ol (2°) (f) 3-Methylbutan-2-ol (2°) (g) Pentan-3-ol (2°) (h) 2-Methylbutan-2-ol (3°) (ii) Primary alcohol: Pentan-1-ol; 2-Methylbutan-1-ol; 3-Methylbutan-1-ol; 2, 2−Dimethylpropan-1-ol Secondary alcohol: Pentan-2-ol; 3-Methylbutan-2-ol; Pentan-3-ol Tertiary alcohol: 2-methylbutan-2-ol Page No 344: Question 11.4: Explain why propanol has higher boiling point than that of the hydrocarbon, butane? ANSWER: Propanol undergoes intermolecular H-bonding because of the presence of −OH group. On the other hand, butane does not Therefore, extra energy is required to break hydrogen bonds. For this reason, propanol has a higher boiling point than hydrocarbon butane. Page No 344: Question 11.5: Alcohols are comparatively more soluble in water than hydrocarbons of comparable molecular masses. Explain this fact. ANSWER: Alcohols form H-bonds with water due to the presence of −OH group. However, hydrocarbons cannot form H-bonds with water. As a result, alcohols are comparatively more soluble in water than hydrocarbons of comparable molecular masses. Page No 344: Question 11.6: What is meant by hydroboration-oxidation reaction? Illustrate it with an example. ANSWER: The addition of borane followed by oxidation is known as the hydroboration-oxidation reaction. For example, propan-1-ol is produced by the hydroboration-oxidation reaction of propene. In this reaction, propene reacts with diborane (BH3)2 to form trialkyl borane as an addition product. This addition product is oxidized to alcohol by hydrogen peroxide in the presence of aqueous sodium hydroxide. Page No 344: Question 11.7: Give the structures and IUPAC names of monohydric phenols of molecular formula, C7H8O. ANSWER: Page No 344: Question 11.8: While separating a mixture of ortho and para nitrophenols by steam distillation, name the isomer which will be steam volatile. Give reason. ANSWER: Intramolecular H-bonding is present in o-nitrophenol. In p-nitrophenol, the molecules are strongly associated due to the presence of intermolecular bonding. Hence, o-nitrophenol is steam volatile. Page No 344: Question 11.9: Give the equations of reactions for the preparation of phenol from cumene. ANSWER: To prepare phenol, cumene is first oxidized in the presence of air of cumene hydro-peroxide. Then, cumene hydroxide is treated with dilute acid to prepare phenol and acetone as by-products. Page No 344: Question 11.10: Write chemical reaction for the preparation of phenol from chlorobenzene. ANSWER: …